The antitumor compound triazoloacridinone C-1305 inhibits FLT3 kinase activity and potentiates apoptosis in mutant FLT3-ITD leukemia cells.

FMS-like receptor tyrosine kinase (FLT3) is expressed in some normal hematopoietic cell types and plays an important role in the pathogenesis of acute myeloid leukemia (AML). In this study, we examined the effects of triazoloacridinone C-1305, an antitumor compound, on AML cells with different FLT3 status in vitro. A panel of human leukemic cell lines with different FLT3 status was used, including FLT3 internal tandem duplication mutations (FLT3-ITD, MV-4-11), wild-type FLT3 (RS-4-11) and null-FLT3 (U937) cells. Cell proliferation was estimated using MTT assays, and apoptosis was studied with flow cytometry and fluorescence microscopy. FLT3 kinase activity (phosphorylation of FLT3 at Tyr591) was determined with ELISA and Western blotting. FLT3 downstream signaling proteins involving AKT, MAPK and STAT5 were examined by Western blotting. RNA silencing was used to decrease the endogenous FLT3. The mutant FLT3-ITD cells were more sensitive to C-1305 than the wild-type FLT3 and null-FLT3 cells (the IC50 values measured at 24 h were 1.2±0.17, 2.0±09, 7.6±1.6 μmol/L, respectively). C-1305 (1-10 μmol/L) dose-dependently inhibited the kinase activity of FLT3, which was more pronounced in the mutant FLT3-ITD cells than in the wild-type FLT3 cells. Furthermore, C-1305 dose-dependently decreased the phosphorylation of STAT5 and MAPK and the inhibitory phosphorylation of Bad, and induced time- and dose-dependent apoptosis in the 3 cell lines with the null-FLT3 cells being the least susceptible to C-1305-induced apoptosis. Knockdown of FLT3 with siRNA significantly decreased C-1305-induced cytotoxicity in the mutant FLT3-ITD cells. C-1305 induces apoptosis in FLT3-ITD-expressing human leukemia cells in vitro, suggesting that mutated FLT3 kinase can be a new target for C-1305, and C-1305 may be a drug candidate for the therapeutic intervention in FLT3-associated AML.